Autoflower Light Cycle – Best Light Schedule For Autoflowering Cannabis
Unlike photoperiods that need at least 12hrs of darkness to trigger flowering, autoflowers automatically enter the flowering cycle when they’re mature enough. They start producing buds based on age thus they don’t depend on darkness to start the flowering cycle.
This means that the best light schedule for autoflowers is either 24/0, 20/4, or 18/6 so there are multiple options and the best one will depend on your growing environment and setup.
Tip: Light cycles are used to simulate seasons in nature, more light = summer, more darkness = winter.
1. What is the best light cycle for autoflowers?
Most growers agree that the optimum amount of light to give autoflowering strains is somewhere between 18-24 hours of light a day. As a grower you should adjust the light depending on the cultivar you’re growing.
There are basically four light cycles aka Light schedules: 24/0, 20/4, 18/6, and 12/12 (the first number is hours of light, the second is hours of dark). You can always adjust the cycle as long as they are receiving more than 12 hours of light a day (to achieve the best results). An example would be 19/5, 16/8, 22/2, etc.
Having that in mind, as mentioned above, there are growers experimenting with schedules like 16/8 but if you’re new to growing you should stick to the basic schedules mentioned above.
Now, despite cannabis plants relying on the amount of light they get, you should know that depending on the phase your plant is in, it will need a different spectrum and that can also affect your harvest.
As you may know, cannabis plants go through 2 stages, the vegetative and flowering stage, during these stages your autoflowers will obviously need light, but they will also need certain wavelengths of the spectrum.
It’s essential you provide the ideal light spectrum for each stage of plant growth and preferably, a full spectrum.
For example, during the vegetative stage, your plants will need a blue spectrum that ranges from around 400 to 550nm whereas during the flowering stage your plants will need a red spectrum, with wavelengths that range from 550-700nm.
This doesn’t mean that you won’t be able to have a successful harvest if you don’t provide a full spectrum but you will definitely have better results by providing the whole spectrum from seed to harvest or at least the spectrum your plants need during each stage.
Have in mind that this applies to all Light fixtures, including light bulbs, usually good-quality LEDs will emit a full spectrum but you can get mixed spectrum bulbs that will get the job done.
2. Do autoflowers need darkness?
There are growers who believe autoflowering plants need a dark period and won’t be as healthy if they get a 24/0 light schedule. There’s no real evidence of that but there may be exceptions. Also have in mind that a 24/0 will lower humidity , increase temperature , and increase the light bill .
Schedules like 18/6 will save you electricity and if the few hours of darkness indeed help the plant to grow better, it’s a win-win. We recommend starting with an 18/6 light cycle and if you see your autoflower has the potential to grow more, you can always try again in the next cycle.
3. 24/0 Light Cycle
Plants usually grow faster when they get more light. This schedule is a good choice if you live in a cold climate, keeping the lights turned on 24hrs a day will keep your autoflowers warm.
Obviously, this is the easiest autoflower light cycle as you don’t even need a timer, just turn on lights until harvest.
- Doesn’t require a timer.
- May result in the best yields.
- Uses more energy, can get expensive.
4. 20/4 Light Cycle
The 20/4 has become a popular autoflowering light schedule amongst growers because it’s in the middle between 18/6 and 24/0, providing a good growth without having to spend too much like when growing under 24/0.
Despite obviously leaving the lights on for a bit longer than in 18/6, your plants still have some time to “rest”, allowing you to have slightly better results without having to spend too much like in a 24/0.
- Allows autoflowers to rest.
- Better results than 18/6.
- Uses more energy than 18/6, can get expensive.
5. 18/6 Light Cycle
This is the most common cycle for autoflowers. You’re providing enough light for your plants to develop and a few hours of dark for them to rest, encouraging healthy growth. This can be good in hot climates.
You can leave your lights at night and have them turn off during the 6 hottest hours of the day. By using this schedule you’ll be using around 25% less electricity, which adds up to be a good economy at the end of every harvest.
A lot of growers who have experimented with 24/0 and 18/6 light cycles say they didn’t notice any major difference in final yield. The only minor inconvenience with this schedule is having to buy and adjust a timer. They cost around 10 bucks so it shouldn’t be a problem at all.
- Allows your plants to rest.
- Uses less electricity, allowing us to save on electricity.
- Can help lower temperatures and increasing humidity in hot climates.
- Requires a timer. This shouldn’t be a problem at all, as this is the first thing you should buy when growing indoors.
5. 12/12 light cycle
The 12/12 schedule is normally used for photoperiods. It can also be used for autoflowers but it’s not that popular. Normally growers give autoflowers this light cycle when they have them growing in the same tent as photoperiods. By giving your autos 12/12 you’re not growing them to their full potential.
Because your plant is getting less light each day, it isn’t able to make as much energy to promote growth. It will underperform compared to the other light cycles, that being said, you can grow them just fine if you don’t mind reduced yields and an overall smaller plant.
- Uses less electricity, allowing us to save on electricity.
- Allows you to grow autos and photos in the same grow tent.
- It’s recommended to grow under 18/6 so 12/12 usually results in aery and underdeveloped buds.
Autoflower grow light schedule pros and cons
|24/0||Faster growth.||May be too much for some strains.|
|20/4||Good growth and allows plants to “rest”.||Slightly less growth than 24/0.|
|18/6||Less heat and cheaper.||Slightly less growth than 20/4.|
6. In Conclusion
There isn’t really a proven best light cycle. Before going for any light cycle, think about electricity costs and the climate you’ll be growing in. If you are in doubt, start with 18/6. This cycle is the most used and should work for all autoflowers.
When growing outdoors you have to work with what you have as you can’t control the sun (obviously). Outdoor growers should be aware that with the change of seasons the amount of daylight may increase or decrease but autoflowers should grow fine in all seasons.
Even though there are the most common light cycles, make sure you experiment with all of them and find what suits you better because every plant and grow setup is different so there’s a chance that you have better results growing under an uncommon light cycle.
What Light Cycle is Best for Autoflowers?
Wondering what’s the best light cycle to grow autoflowers indoors? Check out why specific light cycles work when it comes to autoflowers.
- 1. 24/0 light cycle
- 2. 18/6 light cycle – the best light cycle for autoflowering plants
- 3. 20/4 light cycle
- 4. Do autoflowers need darkness?
- 5. Growing autoflowers outdoors
In the cannabis kingdom, the Ruderalis has the answer to many problems. It’s perhaps the next best thing discovered since flatbread for several reasons. For one, they are fast, and for two, they don’t need a lot of planning.
Photoperiod plants start flowering only when the period of darkness increases, but autoflowers don’t rely on any such signal to do their job. They only produce buds with time, rather than following any particular light/dark cycle.
But, this doesn’t mean they don’t need light at all. Like other plants, they too rely on light to produce food for themselves. Apart from their ability to flower automatically, they are just like regular plants. They require good sunlight or any other lighting source to produce good yields. So, the lighting schedule is an important factor to be considered, especially if you’re growing them indoors.
There’s no particular light cycle used for autoflowers and growers do what suits them the best. Similarly, you can experiment by subjecting the plants to different light cycles and stick to something perfect for you. Read on to understand the best light cycle for autoflowers to produce humongous yields.
24/0 Light Cycle
So, what is an autoflower and what is the best cycle? Many growers believe in providing 24 hours of light for their autoflowers. They swear that it’s the best light cycle since the plants seem to thrive when they receive loads of light. Technically speaking, the plants grow better in a 24/0 light cycle because cannabis can absorb carbon-di-oxide during the process of photosynthesis, making it a C3 plant.
Also, Ruderalis has grown for centuries in the northern hemisphere. In certain areas, it isn’t uncommon for the plants to receive 24 hours of continuous sunlight, and it’s thus possible for autoflowers to do well.
However, what we must not forget is that no matter what type of plant – autoflowers, photoperiod – you grow, they need rest like everything else. Imagine working for 24 hours without a break! All plants need periods of rest where they recover from any damages. Similarly, autoflowers also need their beauty sleep in order to perform well.
Additionally, running the lights for 24 hours at a stretch might reduce the lifespan of the light. Even expensive lights made with high-quality materials may succumb if they are forced to grow for long periods of time without rest. You may not see the difference in the light now, but as time goes by, different issues including heat will crop up all of a sudden.
For growers with extreme climates, it becomes almost impossible to provide 24 hours of light unless an air-conditioner is installed. For instance, if the days get too hot during summer, it’s best to let the plants rest for a while until the temperatures cool down a bit.
And, it goes without saying that you save extra money if you switch off the lights. A few hours every day may not seem like a lot, but it does add up in the long run.
Try growing two plants under different light cycles. While it’s possible for the plant receiving 24 hours to grow vigorously at the beginning, the growth slows down later. With absolutely no period of rest for the plant, the productivity drops down a bit. The difference will also be evident in the yields as plants without rest don’t generate too many buds.
However, it’s important to note that many growers grow plants successfully even after providing 24 hours of light. They believe that the more light the plants get, the better the results. But, while it might work, it’s surely not as productive as the other light cycle described below.
18/6 Light Cycle – The Best Light Cycle for Autoflowering Plants
The 18/6 light cycle is perhaps the most common cycle used by most growers. What makes this schedule perfect is that while it provides more than 14 hours of light necessary for the plant to perform to its fullest potential, it also offers six hours of rest.
With even 6 hours of darkness or resting period, the plant has enough time to recover and grow normally. It’s perfect for beginners that are intimidated by autoflowers. Autoflowers are programmed to grow as quickly as possible and they begin to flourish right from the get-go.
You can’t afford to stress the plant because it becomes difficult for the plant to bounce back. During a 24/0 light cycle, there’s no time for the plant to fight against stress, but an 18/6 cycle provides six hours that can be used by the plant to recuperate.
It’s also beneficial for the lights to rest a bit instead of operating continuously for hours with no breaks. The same logic applies to other appliances such as air conditioners, fans and any other electronic appliances that may be used to control the temperature inside the grow room. With a bit of a breather, the devices will last longer than expected.
Last but not least, you save money even if you reduce only 6 hours of light per day. It equates to a reduction of 180 hours of light per month! Plants in the 18/6 cycle grow extremely well, so you’re cutting down the electricity by 180 hours in a month. And now that you look at it that way, the 18/6 cycle certainly seems like a better option, eh?
So, without a doubt, the 18/6 cycle is perfect for autoflowering cannabis plants.
20/4 Light Cycle
What if you can’t make up mind between 24/0 and 18/6 cycles? You want the plants to grow as much as they can. You’re convinced that the 24/0 is the way to go, but a nagging doubt makes you wonder if it’s overkill. It also logical to think that the plants need some shut eye for at least 6 hours to continue growing the next day.
On the other hand, 18/6 seems too less for you. You’ve got the best equipment and are pretty confident that the lights, fans, and other equipment will sail through without any hiccups. So, what do you do?
For the ones that can’t make up their mind, the 20/4 cycle may be the way to go. While you’re providing ample light, the plants get to rest for 4 hours, so it may just work for you. The best way to find the exact answer is to experiment although an 18/6 cycle seems more sensible.
Optimum light cycles for an Autoflowering Marijuana Strain
One of the best things about growing an autoflowering marijuana strain (or several) is that they are not dependent on light cycles for growth. Plants like Grand Daddy Purp Auto or Blue Dream Auto will start to flower when they reach a certain age or maturity. So as a grower, you don’t need to worry about always turning the lights on or off at a certain time. But still, a cannabis plant is still a plant, and so it’s going to need some type of light in order to thrive. So what light cycles will these plants need to get the best results?
Best light cycles for an autoflowering marijuana strain
It doesn’t really matter what type of strain you have. Whether it’s a Grand Daddy Purp Auto, a Blue Dream Auto, or some other type of auto strain, it’s going to need light and there is an optimum light cycle.
Some growers swear by a 24-hour light cycle for their autoflowering plants. This is simply because cannabis is a C3 plant, it can absorb CO2 during periods of light for photosynthesis. Theoretically autoflowering plants do not actually require a period of darkness and they are also indigenous to northern areas of the world, that do sometimes see periods of 24 hours of light. But that might not be best for autoflowering plants.
A marijuana plant, just like people, need a period of rest and recovery. And when they don’t get it, we can see a negative effect on the yield that they provide and sometimes even pro long or stop them from flowering. Some growers drop the light cycle to 18 hours a day. This for many, including us is considered the optimum light cycle because the plants still get the rest they need while also being given enough light to produce large yields. Other cannabis growers even put their autoflowering marijuana strain in a 20-hour light cycle. These growers believe that this is giving the plant the best of both worlds.
In most cases, no grower wants to give their plants less than 18 hours of light a day. That light is vital to the plant’s growth and without it, the plant and the yield will suffer. But there may be times when a lower light cycle is needed.
When to use the 12-hour light cycle
The Internet is full of forums. And on many cannabis or autoflowering forums, those forums are filled with threads from people asking for advice on why their autoflowering plant isn’t producing the blooms they would like. Sometimes this happens at the time the plant should be flowering, while other times people are simply wondering if they can speed up the already-fast process of getting buds from an autoflowering plant.
Firstly, never rush an autoflowering plant. Nature has already done all the hard work by eliminating the need for several different light cycles and waiting months for the plants to grow enough so they are ready to be harvested. If waiting the short timeframe for an autoflowering plant is too much, it may be best advised that a local dispensary provides the bud that is needed sooner.
But, if you’re being patient and your autos still aren’t producing, there may be something you can do. And that’s switch your plants to a 12-hour light cycle. Even with the experienced growers in these forums, no one really seems to understand why switching the plants to a 12-hour light cycle seems to work. The most logical explanation is that this re-enforces it’s already trained genetics to believe summer is coming to an end, as the plant starts to receive less light. Therefore forcing it to want to grow faster in time to harvest before the frost sets in.
Growers should know that this is a light cycle last resort for when plant appears to not be flowering or is very slow at flowering. It is never advised to lower the light cycle to any more than 12 hours of light per day. That amount will not provide the plant with everything it needs to grow and thrive and is more than likely going to hurt your plant and yield.
An Autoflowering marijuana strain are one of the easiest types of marijuana plants that a person could grow. They’re convenient, they run on their own schedule, and will 99% of the time, flower early with very little muss or fuss. But there are a few things to keep in mind when growing them and these optimum light cycles can help you get yield you hope for.
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